Cell proliferation is a tightly regulated process, with numerous checks and balances imposed by positive and negative regulators of cell cycle progression. Alterations in the levels or activities of such regulators contribute to a variety of processes including differentiation, transformation, and even the induction of programmed cell death. It is becoming increasingly evident that modulations in the activities of many of these cell cycle regulatory proteins are part of the acute cellular response to stress, and directly influence whether a cell will survive or succumb to the treatment. This project is focused on (1) the mechanisms serving to the regulate the activity of cell cycle regulatory proteins during stress and (2) the influence of specific regulatory proteins on the cell~s fate following treatment with certain agents. Studies over the past year have focused primarily on the cyclin dependent kinase inhibitor p21WAF1/CIP1 which has been implicated in G1 growth arrest as well as apoptotic processes. In an initial survey examining the effect of treatment of various cell types with the antiproliferative prostaglandin A2 (PGA2), we found that PGA2 resulted in either G1 growth arrest associated with the induction of p21WAF1/CIP1, or apoptotic cell death accompanied by low expression of p21WAF1/CIP1. To determine whether p21WAF1/CIP1 directly influenced survival we manipulated p21WAF1/CIP1 expression in selected cell types through use of either an adenovirus expression vector to elevate p21WAF1/CIP1 levels, or an antisense p21WAF1/CIP1 expression vector to down- regulate p21WAF1/CIP1 expression. Elevation of p21WAF1/CIP1 was found to enhance survival of PGA2 treated cells, while down-regulation resulted in greater cell death, indicating that p21WAF1/CIP1 exerts a survival influence, at least in response to PGA2 treatment. Current studies are aimed at determining whether p21WAF1/CIP1 exerts a similar influence on survival in response to other stresses, and preliminary evidence with at least one additional stress model, p53-mediated apoptosis in melanoma cells, supports this view.